In recent years, the semiconductor integrated circuit elements (IC chips) used for a CPU in a computer or the like operate at higher speeds, and with higher level functional features, than previously. Along with this advance, the number of terminals has increased and the terminal interval has tended to be narrower. Generally speaking, terminals in large numbers are densely packed on the bottom surface of the IC chip in an array, and a terminal block so formed is connected to a terminal block at the motherboard side by a “flip chip” connection. However, because there is a large difference in pitch between the terminal block at the IC chip side and the terminal block at the motherboard side, it is difficult to directly connect the IC chip to the motherboard. Therefore, the connection method generally employed is one wherein the IC chip is first mounted on a multilayer wiring board and the multilayer wiring board is mounted on the motherboard. Examples of such multilayer wiring boards for mounting the IC chip include a wiring board wherein a core board made of polymer material is formed and build up layers are formed on a top surface and a rear surface of the core board.
FIG. 12 is a schematic sectional view showing a conventional multilayer wiring board.
A multilayer wiring board 100 for mounting an IC chip is comprised of a plate-like core board 101 made of glass epoxy, a buildup layer 102 formed on an upper surface of the core board 101 and a build up layer 103 formed on a lower surface of the core board 101.
The build up layer 102 has a structure in which resin insulating layers 107 made of epoxy resin (i.e., interlayer insulating layer) and conductor layers 108 made of copper are alternately laminated, and an IC chip 110 (semiconductor integrated circuit element) is mounted on the build up layer 102. Similarly, the build up layer 103 has a structure in which resin insulating layers 111 and conductor layers 112 are alternately laminated. The multilayer wiring board 100 is connected to a motherboard 114 through the build up layer 103.
The core board 101 includes a plurality of through hole conductors 116 so that an upper surface and a lower surface of the core board 101 communicate with each other. The through hole conductors 116 are formed by a copper plating, and a hole defined by the through hole conductors 116 is filled with, for example, a plugging body 117, such as an epoxy resin. The through hole conductor 116 is connected to a conductor layers 108, 112 of the build up layers 102, 103. A signal transfer and power supply are conducted between a motherboard 114 and the IC chip 110 through the conductor layers 108, 112 and the through hole conductors 116.
In the multilayer wiring board 100, a through hole conductor 118 for a power supply which penetrates the core board 101 and the build up layers 102, 103 is provided in a peripheral portion of the multilayer wiring board 100. The through hole conductor 118 is formed by a copper plating, and a hole defined by the through hole conductors 18 is filled with, for example, a plugging body 119, such as an epoxy resin.
Japanese Patent Application Laid-Open (kokai) No. H7-50487 (patent document 1) discloses a multilayer wiring board comprised of an inner layer board and an outer layer board, wherein a through hole penetrating the inner layer board and outer layer board is plated by copper. Further, Japanese Patent Application Laid-Open (kokai) No. H11-17341 (patent document 2) discloses a multilayer wiring board comprised of a core material and a copper-clad lamination base material, wherein a through hole penetrating the core material and the copper-clad lamination base material is filled with a conductive paste.
In order for a wiring board 100 to mount an IC 110 chip which operates at higher speeds with high level functional features, it is necessary for the wiring board 100 to supply more electric power to the IC chip 110. However, conventional through hole conductors 116, 118 are formed by applying a copper plating to a through hole. The electric current only flows on an inner circumference face of the through hole. Further, in order to attain a miniaturization of the multilayer wiring board 100, the diameter of the through hole conductor 116, 118 cannot be increased, thereby limiting power supply capacity. Furthermore, although it is possible to increase the power supply capacity by filling a conductive paste (as disclosed in patent document 2) into the through hole to which the copper is plated (as mentioned in patent document 1), the conductive paste has a relatively large electrical resistance, and thus sufficient power supply capacity cannot be secured.
In order to supply high current to the IC chip 110, the number of through hole conductors 116, 118 can be increased. However, it is difficult to secure a space for signal wiring with this method. Thus, another method for securing the sufficient power supply capacity is in demand.
The present invention has been achieved in view of the above problems of the prior art, and an object of the invention is to provide a multilayer wiring board capable of supplying enough electric power to a circuit element, such as an IC chip, and to provide a power supply structure to be embedded in the multilayer wiring board.